let  sleep = (wait)=>{
    return  new  Promise((resolve,reject)=>{
        setTimeout(()=>{
       resolve(wait)
        },wait)
    })
}

//链式回调
sleep(100).then(res=>{
    return sleep(res+100)
}).then(res2=>{
    return sleep(res2+100)
}).then(res3=>{
    console.log(res3);
})


//结论 后面的链会受到前面链的影响